1. Field of the Invention
The present invention relates to a cam follower device incorporated into a valve action mechanism of an automobile engine for minimizing the wear on the parts of the valve action mechanism for a reduction in the noise level of the engine and a reduction in fuel consumption in the engine, specifically to a method and apparatus for securing a shaft of a cam follower device for a valve action mechanism in an automobile engine, so that the durability of the cam follower device is improved, and that the shaft is reliably secured.
2. Description of the Prior Art
Many different types of engines are used in automobiles, but all reciprocating piston type engines, with the exception of some types of two-cycle engines, are provided with intake valves and exhaust valves which open and close in synchronization with the rotation of a crankshaft.
There are many possible configurations for a valve action mechanism for driving the intake valves and the exhaust valves. For example, referring to FIG. 20 which illustrates an SOHC type mechanism, in the case of a four cycle engine, an intake valve 4 and an exhaust valve 5 are reciprocatingly driven through a pair of rocker arms 3, by means of a single cam shaft 2 which rotates at one-half the speed of a crank shaft 1. A pair of cams 6, secured to the cam shaft 2 which rotates in synchronism with the crank shaft 1, drive the intake valve 4 and the exhaust valve 5 reciprocatingly while sliding over one end of the rocker arms 3. It will be understood that the rocker arms 3 receive the movement of the cam 6.
However, in recent years, a cam follower or the like has been provided on the parts of the rocker arms 3 opposite the cams 6, rotating in response to the rotation of the cams 6 to reduce the frictional force between the peripheral surfaces of the cams 6 and the opposing parts of the rocker arms 3, and to reduce the fuel consumption and the like during the operation of the engine.
Specifically, as shown in FIG. 21 and FIG. 22, the opposite ends of a shaft 8 are securely supported in a pair of separated support walls 7 each provided at the end of the rocker arm 3 closer to the cam 6. Specifically, the shaft 8 extends through a pair of through-holes 11 in alignment formed in the support walls 7. At the periphery of the shaft 8 a short, cylindrical rotary member 10 is provided with a plurality of rollers 9 between the shaft 8 and the rotary member 10. The outer peripheral surface of the rotary member 10 contacts the outer peripheral surface of the cam 6 so that the rotary member 10 rotates around the shaft 8 following the rotation of cam 6.
The rotary member 10 converts the sliding friction between the cam 6 and the member opposed to the cam 6, specifically the opposing part of the rocker arm 3, to rolling friction so that the fuel consumption is reduced.
However, as will now be explained there are still problems with this type of cam follower device for a valve action mechanism for an engine, which must be eliminated.
Specifically, in order to operate the cam follower device stably over a long period, the shaft 8 which supports the rotary member 10 must be positively secured so that it does not rotate e.g. relative to the part of the rocker arm 3 opposed to the cam 6.
As the shaft 8 rotates with respect to the abovementioned part, wear gradually occurs at the peripheral surface of the ends of the shaft 8, and at the inner peripheral surfaces of the pair of through-holes 11 formed in the support walls 7 at the end of the rocker arm 3, respectively, so that the shaft 8 is not completely supported due to the wear, and the rotary member 10 tends to lose tight-fitting in the rotation of the cam 6.
For this reason, conventionally, as shown in FIG. 22, the opposite ends of the shaft 8 are interposed in an interference fit relationship in the through-holes 11, and in addition, a tool member, as shown in FIG. 23 and FIG. 24, is used in order that both ends of the shaft 8 are attached by caulking or crimping at the inner peripheral surfaces of the through-holes 11 so that the shaft 8 is not rotated relative to the support walls 7.
However, when rotation is prevented by using this type of simple caulking or crimping, there is concern that the shaft 8 will turn when a large force is added to the shaft 8 because the rotation of the shaft 8 in the support walls 7 is prevented only by the force of friction on the caulked or crimped portion.
In addition, when the shaft 8 is prevented from turning by caulking or crimping the both ends of the shaft 8, it is necessary that the depth of the caulking or crimping be strictly controlled. If the depth of the caulking or crimping is inadequate the shaft 8 is not properly prevented from turning, and, conversely, when the depth of the caulking or crimping is too great, the outer periphery of the mid portion of the shaft 8, where the rollers 9 contact, are deformed so as to decrease the durability of the rollers 9. Such problems are experienced in a conventional tool member for securing a shaft of a cam follower device as shown in FIG. 23 and FIG. 24, specifically when the conventional tool member is used, the force which acts against the tool member gradually increases during the caulking or crimping operation, so that it becomes difficult to strictly control the depth of the caulking or crimping.
In existing automobile engines, the force applied is not strong enough to rotate the shaft 8, but in recent years high rotation and high output engines have been provided, and there is also a tendency toward increased power application to the shaft 8. Therefore, to cope with the higher rotational speeds and higher outputs expected in the future, measures are required to more reliably prevent the rotation of the shaft 8.
As a means of eliminating this type of problem, in Japanese Utility Model First Publication No. 64-34406, as shown in FIG. 25 to 28, it has been proposed that the shaft 8 be prevented from rotating by caulking or crimping the end of the shaft 8 in the shape of a non-concentric circle relative to the shaft 8. However, with this type of conventional structure, the caulking or crimping must be deep to actually prevent the rotation, and because it is not easy to caulk or crimp the end of the shaft 8, not only is the cost of fabricating the cam follower high, but there is a tendency for the center portion of the shaft 8 being deformed by the effect of the caulking or crimping. When the center portion of the shaft 8 is deformed by the caulking or crimping, the life of the roller bearing, in which the outer peripheral surface of the shaft 8 is used as an outer track, is undesirably shortened.
Also, in Japanese Utility Model First Publication No. 63-133851 a method is disclosed wherein only one part of the end surface of the shaft 8 is caulked or crimped at the edge of the opening of the through-hole 11 using the previously described technique, but the same type of problems are produced.